Long term trends of halogenated trace gases, hydrocarbons, alkyl nitrates and of the oxidative capacity of the atmosphere

• Main Author: Newland, MJ
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Arctic; Greenland; Grim; GRIP
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/49485/; https://ueaeprints.uea.ac.uk/id/eprint/49485/1/Mike_Newland___Long_term_trends_of_halogenated_trace_gases,_hydrocarbons,_alkyl_nitrates_and_of_the_oxidative_capacity_of_the_atmosphere___June_2014.pdf

Atmospheric trends of a series of ozone depleting substances (halons) and greenhouse gases (PFCs, SF5CF3, HFC-227ea) are reported using measurements from Cape Grim, Tasmania. A two-dimensional global atmospheric chemistry transport model is used to derive global annual emission histories of these long lived gases. Emissions of the halons are found to have decreased since peaking in the 1990s. There is still some considerable uncertainty in the remaining banks of the halons caused by uncertainties in their atmospheric lifetimes and possibly in the reported production data. The contribution of the halons to total tropospheric bromine is predicted to fall from current mixing ratios of about 8.1 ppt to about 3 ppt by 2060 assuming reported lifetimes to be correct. Emissions of the higher perfluorocarbons (PFCs) (C4F10, C5F12, C6F14 and C7F16) have decreased since peaking in the 1990s, with the exception of C7F16, emissions of which have remained stable since the 1990s. Emissions of C3F8 have also decreased since the 1990s; those of C2F6 appear to be increasing though this disagrees with recent work of other groups. However the growth rate of the radiative forcing of the atmosphere from the PFCs reported herein has been relatively constant for the past decade largely because of increasing emissions of c-C4F8. Emissions of SF5CF3 appear to have ceased in the mid-2000s seeming to confirm the source of the gas as being from production of certain fluorochemicals by the company 3M. Emissions of the hydrofluorocarbon (HFC) HFC-227ea have increased rapidly since the mid-1990s. Long term trends of six alkanes (ethane, propane, n-butane, iso-butane, n-pentane and iso- pentane) and six alkyl nitrates (methyl, ethyl, 2-propyl, 2-butyl, 2+3-pentyl and 3-methyl-2- butyl) have been derived from measurements from firn air from the two Greenland sites, NEEM and North GRIP. These suggest that alkane mixing ratios peaked in the Arctic around 1980 and that alkyl nitrate mixing ratios in the Arctic peaked in the early 1990s. A detailed ...